1. Field of the Invention
This invention relates a photosensitive resin film excellent in workability and usable as a film resist, as well as to a process for producing a laminate by use thereof.
2. Description of the Prior Art
Film resists are mainly used as etching resist or plating resist for forming a conductor pattern in the production of printed circuit boards. As such a film resist, "Riston" (a trade name of Du Pont Co.), "Laminar" (a trade name of Dynachem Corp.), and "Hitachi Photosensitive Resist Film" (a trade name of Hitachi Kasei Kogyo K.K.) are commercially available. They are all composed of an acrylate polymer, an acrylate monomer, a storage stabilizer, a dye and a photo-polymerization initiator. These compositions are soft and sticky because of containing an acrylate monomer, so that they are handled in the form that they are put between a support film, such as a polyester film, and a protecting film, such as a polyolefin film. Nevertheless, these compositions have faults that, even if handled in the above-mentioned form, the compositions protrude from both sides of the support film after a long-term storage at high temperatures to injure the openability of film, that the acrylate monomer has a characteristic unpleasant odor, that a photomask cannot be brought into intimate contact with the photosensitive layer when printing the image because of the stickiness of the layer, and hence the printing has to be done through intervention of the support film so that a sharp image is difficult to obtain, that the photo-crosslinked film is brittle and the image produced by photo-crosslinking is apt to be disfigured, that the film lacks adhesion to the solid surface on which an image is to be formed, and that entrapment of air tends to occur at the time of lamination.
Apart from etching resist and plating resist, there is included a solder resist for printed circuit board in the field using a resist in the form of a film. Hitherto, in permanently protecting or soldering circuits in the printed circuit board industry, a solder resist has been used for the purpose of hiding the parts of circuit requiring no soldering with a resist coating film, thereby preventing the solder bridge between circuits. In this case, heat resistance is needed so that a commercially available etching or plating resist cannot be, as it is, used as a solder resist. Commercially available films for solder resist are also photosensitive compositions of acrylate type, which have the same faults as the above-mentioned dry film resists for etching resist and plating resist have and, at the same time, are insufficient in heat resistance.
The present inventors have conducted extensive research with the aim of overcoming these faults of commercially available film resists to discover a novel photosensitive resin film by which all the above-mentioned faults can be overcome and which can be used as any of the etching resist, plating resist and solder resist. If a printed circuit board is manufactured from it, the steps are simplified and a sharp image can be obtained, so that the photosensitive resin film of this invention contributes much to the industry.